Saturday, 19 June 2010

Rodents of Bristol 2: The Giant Rat of Madagascar

Although the Madagascar is famous for its lemurs, and to a lesser extent its reptiles, many other groups are either entirely or nearly entirely confined to the island. Among these are a very diverse group of rodents, the Nesomyids. Although clearly related to the giant rodent family Muridae, which includes the common pests of house mouse and brown rat, all the endemic Malagasy rodents form a single clade, which probably originated from a single colonization from Asia and subsequently diverged into the 21 species (at least) in nine genera that are known today.

Given that the number of species of lemur that have been identified in recent years, the comparative lack of study of the rodents, and the widespread habitat destruction in Madagascar, it seems likely that many more species have either recently become extinct or await discovery.

Madagascan rodents occupy every available habitat, from dry spiny forest to rainforest, and vary in size and habitat from the gerbil-like Macrotarsomys up to the 1.5kg subject of this article, the Giant Jumping Rat or Votosvotsa Hypogeomys antimena.

Giant jumping rats are found today in the dry deciduous forests of western Madagascar, especially around the town of Morondava. Although there is now only a single species of Hypogeomys, a second form, H.australis, is known as subfossil remains from the south east of the island.

Like most rodents, especially the larger ones, they are vegetarian, feeding on seeds, nuts and fallen fruit. Food is held in the front feet and nibbled like a squirrel.

It will come as no surprise that the Votsovotsa lives in burrows. These house a monogamous pair plus their offspring, and can extend many metres and be half a metre in diameter. A single family will use 7-8 acres 93-4 hectares) of forest the territory is marked by scent, although I have not found any description as to how it is defended against intruders.

Young (usually 1 or 2) are born at the start of the rainy season in late November, and young will stay with the parents for at least 1 or 2 years (more for young females). The main predators aside from human beings are the Fossa, which fills the big cat niche in Madagascar (although it is actually a mongoose) and the larger native snakes.

The current wild population is estimated at around 11,000, but with current rates of habitat loss and the restricted range it is classed as Endangered. There are some in zoos, but ISIS currently lists only 70 individuals, although they are now being bred (15 births in the last 12 months). Bristol has bred 4 of these, and our group will probably continue to produce young which can be distributed to other collections. In the US they are held at Bronx Zoo, Prospect Park, Philadelphia, and Omaha.

They seem to mix well with other species – we have one family on show with Mouse lemurs in Twilight World where they have bred, and we have mixed others with our lemurs in the Lemur Walk Through exhibit. These latter remain inside and are not seen by visitors, but it enables us to make best use of available space. I have seen them mixed with Aye Aye at Jersey, but am not sure if they are still there.

(image from Wikipedia)

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